1. Field of the Invention
The present invention relates generally to an uninterruptible power supply (“UPS”) and more particularly to a UPS that has an adjustable reserve power level that can provide power to attached load devices when the input power source drops below a user selected threshold voltage level for more than a minimum time interval.
2. Description of Related Art
A large number of electronic devices require continuous power for proper operation. For example, computers must receive continuous power in order to avoid costly down time, and more importantly, prevent the loss of data. In an Internet-based telephone system, such as Voice over Internet Protocol (“VoIP”), power is usually furnished to the telephone system through an AC power line or AC mains. However, during power outages, it can become critical that the telephone system operate reliably using an auxiliary power source such as a UPS in case of emergencies. It is desirable to eliminate unforeseeable power line disturbances ranging from deviations from the specified line voltage known as “Brown-outs” or “Brown-power” to complete power loss to provide continuous power to electronic devices and/or computers.
Moreover, since AC power line failures occur rather infrequently, a user often is unaware of the current state and reserve power capacity of the internal battery of the UPS. Thus, it is important that the current reserve capacity of the UPS be known in advance of the UPS switching over to this backup power source during a time of power outage, so she can plan accordingly regarding use of devices (e.g., the VoIP telephone system) connected to the UPS. It is also important to advise the user how much reserve time capacity remains while the VoIP system is operating on reserve battery power from an auxiliary power source such as a UPS. Further, it is desirable to provide the user with accurate estimates of remaining time while connected devices to the UPS are running on auxiliary power. Further still, it is important to advise the user when to replace the battery due to insufficient reserve capacity, rather than make this determination when there is no alternative power source available.
A common type of UPS utilizes an array of on-board storage devices or batteries to supply reserve power when there is a line disturbance or power shortage on the power source line. These are commonly known as a “standby UPS” or offline UPS design. These storage devices only provide adequate power for a single short period of time before the internal battery needs to be recharged. Therefore, an immediate switch from AC main power to reserve power from the internal battery when the AC main power line voltage sags below a threshold value may result in premature depletion of available battery power.
Another common type of UPS is designed so that an AC to DC inverter is always connected to the output line of the UPS. This design is known as a “line-interactive UPS.” When the AC input power is present, the inverter operates in reverse to charge the internal batteries. When AC input power fails, the UPS reverses the power flow from the inverter and provides power to the load. This design provides better filtering than a standby UPS, because the inverter is always connected to the load. But, the line-interactive UPS still suffers from the drawback of the storage devices only providing adequate power for a single short period of time before the internal battery needs to be recharged.
There are situations in which it would be useful for a UPS to either have two or more separate reserve power supply sources or the ability to reserve or hold back a portion of the battery reserve power from one or more reserve power supply sources. This way, after the initial battery reserve power is exhausted, the user can again activate the UPS to supply an additional second period of reserve power to the attached devices. For example, the user may need to send or check her email on her computer and just needs to power up or activate her computer for a short time or she needs the ability to access the Internet on her computer to accomplish a task before the AC power source is restored. One area of growing importance is with respect to VoIP systems as mentioned above, wherein the user wants to be able to make telephone calls over the system when the AC power source has failed. The VoIP utilizes the user's Internet hub, router, cable modem, and/or ADSL modem, which are often powered by the AC mains. This can be critical in the case of an emergency where the user urgently needs to call the fire, police department, ambulance or 911 service and the like.
Accordingly, there is a need for a UPS design that gives the user the ability to adjust the reserve power level of the battery or on-board storage device so that she can later reactivate the UPS and use an attached electronic device after the initial reserve power supplied has been exhausted. Additionally, the ability of the UPS to provide the user with an accurate estimate of the backup power available from the internal battery, taking into account the attached device load, would allow the user to properly adjust the reserve power level to provide adequate power to reactivate the UPS when a user demand for backup power is received.